SENT bus serial protocol decoding

Wiring

SENT bus requires just one signal line in addition to the 5 V supply and ground lines.

Signaling

Data is normally transmitted as two 12-bit data words in a message frame. SENT uses ticks as units of time. One tick is typically 3 µs.

A SENT message starts with a synchronization pulse where the time between successive falling edges is equivalent to 56 clock ticks.

After the synchronization pulse the Status/Communication bits communicate status and/or slow channel data  depending on the SENT format.

Data is transmitted in units of 4 bits, or "nibbles". Within a nibble, the initial logic 0 time is a fixed width of 5 ticks or more, which is followed by logic 1 with a variable duration. The total nibble time encodes 4 bits of data in the measured number of tick units. 12 ticks duration = binary 0000 (Hex 0), 13 ticks = binary 0001 (Hex 1), 14 ticks = binary 0010 (Hex 2) and so on up to 27 ticks = 1111 (Hex F).

A pause pulse may be inserted at the end of each message to fill up the message to a fixed length not exceeding 1 ms.

SENT decoding with PicoScope

The first step is to acquire the SENT signal of interest using PicoScope. Then select Serial Decoding from the Tools menu.

Click Create and select SENT from the list of available protocols.

In the SENT configuration dialog select the PicoScope Data input channel, Tick Time, Sensor Type, and other parameters as necessary.

Click OK to see the decoded SENT messages in the PicoScope graph display.

If you check the In Table box, PicoScope will display SENT messages in a tabular listing format. Double-click a message in the table to see the same message in the graph display.

Simultaneous decoding of SENT Fast and SENT Slow channels

PicoScope can simultaneously decode SENT Fast and SENT Slow channel messages that are transmitted on the same line.

Slow channel data is sent two bits at a time within the standard SENT message frame. So for each fast channel message frame the transmitter can also include two bits of slow channel data: bit 3 and bit 2 of the status nibble. The purpose of the slow channel feature is to allow up to 32 slow channel messages per serial message cycle to be transmitted with minimal impact on the primary sensor data. Slow channel messages can be used to continually monitor information such as temperature, diagnostics and production codes, which either do not change or change at a slower rate than the primary sensor data.